Deficient BDNF signaling has been associated with extinction failure and with a poor response to extinction- based therapies for PTSD. Deficient hippocampal-prefrontal connectivity has been correlated with PTSD severity. Our recent work in rats suggests that BDNF signaling from the ventral hippocampus (vHPC) to the infralimbic prefrontal cortex (IL) modulates fear extinction. Much of what we understand about the emotional regulation related to PTSD comes from experimental fear conditioning and extinction, which model the hyperarousal and re-experiencing of symptoms of PTSD. Much less is known, however, about excessive avoidance seen in PTSD. In Aim 1, we will investigate the role of BDNF signaling in extinction of avoidance. In Aim 2, we will improve BDNF signaling to facilitate extinction in rats unable to extinguish avoidance responses.